The present invention relates to an article for establishing a seal between two substrates, more particularly to such an article having a plurality of layers, and even more particularly to such an article having a plurality of sealant layers with an outer adhesive layer having a different curing rate than the remaining layers.
This invention relates to establishing a seal between two substrates. When attaching two substrates to each other, it is often important to provide an adhesive or sealant that sufficiently wets over the bonding surface, prior to bond formation. The degree of wet-out over the contact surface typically impacts the bond strength. The integrity of the seal can depend upon the proper adhesive strength and the cuing properties of the adhesive used in forming the seal. An appropriate surface contact between the adhesive and the substrate will enable a strong seal between the two substrates and thus prevent leakage through the bond line.
The integrity of the seal is particularly important where at least one of the substrates is glass. Many applications exist where it is necessary to secure a glass substrate within a frame such as a metal, plastic or wood frame, which may be painted. For example, a glass windshield or glazing is secured within the metal or plastic frame of a motor vehicle both during vehicle manufacture and during the replacement of damaged windshields on motor vehicles.
Polyurethane pastes are conventionally used to establish a seal between the primed glass and the frame. Such pastes, however, are difficult to apply uniformly and reproducibly. Additionally, such materials involve the undesirable use of wet chemistry, or solvent-based compounds, at the point of application. Another problem is that pushing the glass into the frame causes the paste to flow and squeeze out of the bond line. This creates bond lines of uneven thickness and glass-frame contact points that can act as failure points because any stress applied to the frame is transmitted directly to the glass at these points.
Another problem is encountered in the case of polyurethane sealant pastes that require a relatively long time to cure and build bond strength such as those which are moisture curable. During this vulnerable curing period, the glass can vibrate within the fame, making the seal and the glass susceptible to damage. Gaps in the seal can form, giving use to wind noise and compromising seal integrity. The noise associated with the vibrations is also undesirable. Moreover, the reliance on ambient moisture means that the cure process varies depending upon ambient conditions.
Thus, there is a need for a sealant that does not exhibit the above-described problems.
The invention features a multi-layered sealant for use in establishing an adhesive bond between two substrates. The article includes a photo-activated, epoxy-containing bulk layer. The bulk layer has a first major surface on which is bonded an adhesive layer. The adhesive layer is also a photo-activated, epoxy-containing material. Upon photo-activation, the at least one bulk layer has a different curing rate than the adhesive layer.
The difference in curing rate for the adhesive layer and the bulk layer is accomplished by adjusting the formulation of the compositions, the thicknesses of the layers, the activation parameters, the cure kinetics, or combinations therefore. The curing rate is measured through conventional techniques, such as thermal analysis, chemical analysis, and spectroscopy analysis.
The difference in curing rate is adjusted to accomplish an improved adhesion to substrates over single layer sealant compositions. The individual layers can be formulated to obtain improved wet-out onto the contact surface of the substrate and still obtain strong adhesive properties over a relatively short period of time.
Optionally, the multi-layered article of the present invention can include other layers applied onto a second major surface of the bulk layer. These optional layers are applied onto the bulk layer on a surface opposite the adhesive layer. The optional layers are application dependent and can serve as spacers, insulating layers, or bonding layers.
It is an advantage to provide an article that utilizes solid materials to form a seal between substrates. A solid article eliminates the use of wet chemicals and the material handling issues associated with them. It is also an advantage to utilize a sealant composition that provides sufficient wet out while quickly building adhesive strength over time. The ability to wet-out enhances the adhesion after complete cure of the polymeric material. The ability to build adhesive strength over a short period of time enables the use of the sealant in time demanding applications, such as, for example, the installation of the windshield in a motor vehicle.
For purposes of the present invention, the following terms used in this application are defined as follows:
xe2x80x9cphoto-activationxe2x80x9d means application of sufficient actinic energy to initiate the polymerization or cure;
xe2x80x9cinitiatorxe2x80x9d and xe2x80x9ccatalystxe2x80x9d are used interchangeably and mean a material that can change the speed of a chemical reaction;
xe2x80x9ccationically curable monomer or resinxe2x80x9d means at least one epoxide containing material;
xe2x80x9cpolymerizable compositionxe2x80x9d or xe2x80x9ccurable compositionxe2x80x9d as used herein means a mixture of the initiator system and the cationically curable monomer; polyols and adjuvants optionally can be present;
xe2x80x9cpolymerizexe2x80x9d or xe2x80x9ccurexe2x80x9d means to supply sufficient energy to a composition in the form of at least actinic energy to alter the physical state of the composition, to make it transform from a fluid to less fluid state, to go from a tacky to a non-tacky state, to go from a soluble to insoluble state, or to decrease the amount of polymerizable material by its consumption in a chemical reaction;
xe2x80x9cPhoto-initiatorxe2x80x9d or xe2x80x9cinitiator systemxe2x80x9d means being capable of initiating polymerization;
xe2x80x9ccure ratexe2x80x9d means the time elapsed from initial activation to cessation of further consumption of epoxy at a given temperature;
xe2x80x9cacceleratorxe2x80x9d means at least one of a specified class of compounds that moderate the cure of a composition of the invention;
epoxy-containingxe2x80x9d means a material comprising at least one epoxy and can further comprise accelerating additives, stabilizing additives, plastic fillers, polyols, thermo-plastic inhibitors and other additives;

xe2x80x9csensitizersxe2x80x9d mean compositions that broaden the spectral response of photosensitive compositions;
xe2x80x9cgreen strengthxe2x80x9d means initial holding power of the polymeric article to a substrate either before or after initial curing; and
xe2x80x9cwet-outxe2x80x9d means the ability of the adhesive to spread out over and bond to the contact surface prior to reaching a cured state.
Other features and advantages will be apparent from the following description of the preferred embodiments thereof, and from the claims.